The present invention relates to electric protective means for overcurrent protection and electric leakage protection, and more particularly to such an overcurrent and electric leakage protective circuit means designed for use in an electric socket, an electric extension cable, etc.
An improper use of an electric apparatus may cause a short circuit, resulting in a fire. Electric extension cables with overcurrent protection devices are well known. These conventional overcurrent protection devices are commonly of mechanical type. These mechanical type overcurrent protection devices are less sensitive. If the user touches the positive and negative terminals of the power circuit by an error when using an electric extension cable or electric socket having a mechanical overcurrent protection device, or when an electric leakage occurs due to an insulator damage of the load such as motor, electric heater, air conditioner, electric ventilator, refrigerator, etc., the mechanical overcurrent protection device cannot automatically cut off power supply. Further, when several electric apparatus are simultaneously used, causing an overload or short-circuit, a fire accident may occur if the fuseless switch of the electric distributor does not break to cut off power supply from the loads.
The present invention has been accomplished under the circumstances in view. It is one object of the present invention to provide an overcurrent/short circuit protection circuit for an electric apparatus, which is of electronic design that automatically cuts off power supply within few microseconds after the occurrence of an overcurrent/short circuit. It is another object of the present invention to provide an electric leakage protection circuit for an electric apparatus, which automatically cuts off power supply when an electric leakage or electric shock happens. According to the present invention, the overcurrent protection circuit comprises an AC relay, a SCR (silicon controlled rectifier) which controls the AC relay, a trigger circuit which drives the SCR, a constant current detector served as a triggering signal source for the trigger circuit, and an alarm device, the AC relay having a common contact connected to a first power line, a normal close contact for electric current output of the first power line to which the common contact is connected, and a normal open contact bridged to a second power line through the alarm device. According to the present invention, the electric leakage protection circuit comprises an AC relay, a SCR (silicon controlled rectifier) which controls the AC relay, a trigger circuit which drives the SCR, a micro current detection amplifier served as a triggering signal source for the trigger circuit, and an alarm device, the AC relay having a common contact connected to a first power line, a normal close contact for electric current output of the first power line to which the common contact is connected, and a normal open contact bridged to a second power line through the alarm device.